Improve masthead text wrapping

Stop 'Marlin-2B' breaking across lines

Tiles get the same playing state as results; balance heading wrap

Masthead: name the model, drop 'watched'

Opening grid: always a complete last row

Add 'Why this exists' block below results

Codex review fixes: in-panel seeks no longer wipe the shot list; requested-vs-loaded race; retry state machine; paused-state sync; touch targets; dvh + scroll containment

Replace Gradio Blocks with gradio.Server: own HTML shell, own CSS, no selector rewriting